Recent magnetic disk devices include a function of changing a level of write current (write current value) according to a data pattern of write data. This function is called data dependent write (DDW), a pattern dependent write (PDW), or the like. In a magnetic disk device not equipped with this function, a head amplifier IC (preamplifier) outputs a uniform write current, which corresponds to a data pattern of write data output from a read/write (R/W) channel, to a head. By contrast, the magnetic disk device having the DDW or PDW function needs to synchronize signals for changing a value of the write current at least in the head amplifier IC according to the data pattern of the write data.